The state of the art, as disclosed for example in GB-A-2.352.954, includes synchronous brushless linear electric motors of the general type as described above. Such motors comprise a mobile part which normally consists of an armature or frame on which the housing compartments are made, normally equidistant, inside which electric coils associated with feed means are inserted and clamped.
A relative fixed bar, normally made of ferromagnetic material, is present in a position facing at least one side of the armature; a plurality of permanent magnets are mounted on the fixed bar, arranged aligned and usually equidistant in the direction of movement of the armature which carries the electric coils. The magnets have alternating polarities.
In other constructional embodiments, the motor can have the fixed part comprising the electric coils and the mobile part comprising the permanent magnets.
The armature where the coils are housed and the ferromagnetic bar on which the magnets are mounted are separated from each other by an air interspace.
The working principle of linear motors of this type exploits the force of repulsion which is created by sequentially inverting the direction of circulation of the electric current circulating in a coil every time the coil moves from a position facing a magnet with a certain polarity, for example, positive, to a position facing a magnet with a negative polarity.
In conventional motors (see for example U.S. Pat. No. 6,140,734), the coils are buried in an insulating material, for example resin, inside the respective housing compartment of the armature, and are cemented in the furnace by means of heat treatment which causes the resin to be activated (melted) and penetrate between the spirals of the coil. The insulating material is necessary to eliminate phenomena of magnetic friction between adjacent coils which cause a deterioration to the performance of the motor.
The insulating material, having set between the spirals of the coil, also acts as a mechanical support for the stable housing of the coils in the relative compartments of the armature, in order to ensure a precise positioning with respect to the fixed magnets.
However, it has been found that using a hot cementing process on insulating material causes a lack of mechanical rigidity due to the interstices between the spirals which are not completely filled, particularly in the inner compartment of the coils. When the motor is used at high frequency conditions, in the long term mechanical stresses are created on the coil which lead to a loosening of the spirals which are thus exposed to the environment, with negative repercussions on the functioning and efficiency of the motor.
The presence of interstices between the spirals causes a deterioration in the interaction conditions of the magnetic fields produced respectively by the current circulating in the coils, and by the permanent magnets, with a reduction in the value of the force of repulsion which drives the motor.
Moreover, the presence of insulating material functioning as a mechanical support for the coils determines a low capacity to dissipate the heat generated by the Joule effect, with consequent problems of overheating in the armature of the coils.
The present Applicant has devised and embodied this invention to solve the shortcomings of the state of the art, and to obtain further advantages.